🐷 Savings Calculator (Monthly Deposits)
Put in the same amount every month and see what you have at maturity. It also shows why a "5% savings plan" earns about half of what you might expect.
Maturity value (after tax)
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How to use
- Choose your currency and enter how much you'll deposit each month.
- Enter the annual interest rate and the term in months.
- Pick simple interest (most fixed-term installment savings accounts, such as Korean 적금 and Indian recurring deposits) or monthly compound.
- Set the tax on interest. Use 0% to see pre-tax numbers, 15.4% for a standard Korean account, or your own marginal tax rate (for example 22% or 24% in the US).
Why monthly savings earn less than you think
When you deposit monthly, only the first deposit earns interest for the whole term, and the last deposit earns just one month. So a 12-month plan at 4% earns roughly half of what the same total would earn as a lump sum at 4%. The "same as a lump-sum deposit at" row shows this effective rate. For a 1-year plan it's about 2.17% when the advertised rate is 4%.
Formula
- Simple interest:
interest = monthly deposit × (rate ÷ 12) × n(n + 1) ÷ 2 - Monthly compound: each deposit k grows to
deposit × (1 + rate/12)n − k + 1, and the results are summed.
Example: $500 a month at 4% for 12 months
| Item | Amount |
|---|---|
| Total deposits | $6,000.00 |
| Interest (simple, pre-tax) | $130.00 |
| Same $6,000 as a lump sum for 1 year | $240.00 |
Tax on interest
- South Korea: 15.4% (14% income tax + 1.4% local tax) is withheld from bank interest. Some cooperative accounts are taxed at 9.5%, and qualifying tax-free accounts at 0%.
- United States: bank interest is taxed as ordinary income at your federal (and state) bracket. It's reported on Form 1099-INT and is not withheld by default.
- Tax-advantaged accounts (IRA, ISA, Korean ISA) can lower or defer the tax.
Banks differ in how they count days and deposit dates, so actual interest may vary slightly. Check any bonus-rate conditions before signing up. For a lump sum plus monthly contributions over many years, use the compound interest calculator.
FAQ
If the savings plan pays 5%, do I earn 5% on my money?
No. Because money goes in monthly, the average balance is only about half the total deposits. A 1-year plan earns about half the interest of a lump-sum deposit at the same rate.
Simple or monthly compound — which pays more?
Monthly compound pays slightly more at the same rate, but over 1 to 2 years the difference is small. It matters more over long terms.
How much tax is taken from interest in Korea?
The standard rate is 15.4% (14% national + 1.4% local income tax). Some tax-favored accounts are 9.5%, and qualifying accounts can be tax-free.
Is savings interest taxable in the US?
Yes. Interest is ordinary income, reported on Form 1099-INT, and taxed at your marginal federal rate plus any state tax. Enter that rate in the tax field to estimate what you keep.
What does “same as a lump-sum deposit” mean?
It is the annual rate a one-time deposit of your total contributions would need to earn the same interest over the same term. It shows the real yield of a monthly plan.